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Ahhhh...... The Generator versus the Alternator......

From: Mike B
Remote Name:
Date: October 01, 2003


Dario, You have discovered why the generator was replaced with the alternator..... low output at idle and low speed. This, coupled with accessories running too, caused a lot of battery's to die. A good 12 volt battery, no load, fully charged, should indicate a voltage of 13.8 VDC (this is it's "float" level). A lead acid car battery should never be charged at more than 14.2 VDC or boiling of the electrlyte will occur. Also, most battery manufacturers recommend that the battery never be given a chargeing current of more than approximately 10% of it's stated amp-hour rating (sometimes hard to know these days of rating batteries by cold cranking amps or CCA. A good battery shop can tell you the amp-hour rating though). So if you have a 650 amp-hour battery, the maximum charging current permissable should not exceed, ever, 65 amps. Even this should not be maintained for long as it will heat up a battery. Your reading of 13.45 in a revved situation seems low to me because at this rate, you can never achieve float, therefor sulfation will occur, in time killing your battery. However, you don't say where you actually measured the output... at the generator output post or at the actual battery post? It can make a difference, and you should really check both places, using the battery common for both readings. Try it with and without headlights on, to provide a load. If there is a significant difference between the post and battery, you may have some fittings to repair. If you can not, even with a somewhat discharged battery, achieve when revved something closer to 14 VDC at the battery, then you can suspect and possibly adjust your regulator. Hope this helps you out, Dario. Mike


Last changed: July 19, 2018